In many image processing apparatuses, an image is first stored in a frame buffer before being output to a display. To reduce a buffer capacity, some image processing apparatuses are configured to compress an image before storing the image in the frame buffer.
A typical display is configured to scan images successively in a horizontal and forward direction (i.e., from left to right) (hereinafter the horizontal and forward direction of the display will be referred to as a “scanning direction”). To output a video signal on the display, the image processing apparatus successively expands the compressed image stored in the frame buffer in a horizontal and forward direction (hereinafter the horizontal and forward direction of the image will be referred to as a “line direction”).
In recent years, more image processing apparatuses capable of outputting rotated images have been increased. A tablet terminal, for example, can display a rotated image in accordance with the rotation of the display.
In the case of the image processing apparatus that does not output the rotated image, the scanning direction of the display always matches the line direction of the display image. The image processing apparatus, therefore, can output a video signal in the scanning direction only by successively reading the image from the frame buffer along the line direction.
However, in the case of the image processing apparatus capable of outputting the rotated image, the scanning direction of the display does not match the line direction of the display image when the rotated image is output. For example, if the display image is rotated by 90 degrees, the scanning direction and the line direction become orthogonal to each other. If the display image is rotated by 180 degrees, the scanning direction is opposite to the line direction. The image processing apparatus capable of outputting the rotated image, therefore, needs to read the image stored in the frame buffer not only in the line direction but also in other directions in order to output the video signal in the scanning direction.
To allow reading in other directions, the image stored in the frame buffer may preferably be a non-compression image. However, this causes the non-compression image to be held in the frame buffer, such that the image processing apparatus needs to include a large capacity frame buffer. The large capacity frame buffer may increase product cost.